Field of the Invention
The present invention relates to a toner for developing electrostatic charge images. In particular, the present invention relates to a toner for developing electrostatic charge images, the toner having superior charging properties and high durability, exhibiting high compatibility between low-temperature fixing properties and thermal resistance during storage, exhibiting improved releasability by efficient elution of a release agent from toner particles during fixation for high-speed printing, and providing images with consistent gloss.
Description of Related Art
Recent electrophotographic image forming apparatuses require toners for developing electrostatic charge images (hereinafter may be referred to simply as “toner”) having superior low-temperature fixing properties in view of high printing rate and further energy saving for a reduction in environmental load. Such a toner requires a reduction in melting temperature or melting viscosity of a binder resin contained in the toner. Several documents propose toners containing crystalline resins (e.g., crystalline polyester resins) as fixing aids and thus having improved low-temperature fixing properties.
Unfortunately, toner matrix particles consisting of only core particles exhibit poor thermal resistance during storage. Thus, a toner has been proposed which has a core-shell structure composed of core particles exhibiting low-temperature fixing properties and shell layers exhibiting thermal resistance during storage, the core particles being coated with the shell layers.
Unfortunately, in the toner including a core particle and a shell layer composed of different resins, the compatibility between the core particle and the shell layer is lower than that in the case where the core particle and the shell layer are composed of the same resin, and small discrete segments of the shell layer lie on the surface of the core particle (refer to, for example, Japanese Patent Application Laid-Open Publication No. 2012-194314). Thus, the core particle has many exposed portions, resulting in insufficient thermal resistance during storage. In addition, the core particle cannot be evenly coated with an external additive because of the rough surface of the toner. Thus, the toner may fail to exhibit satisfactory charging properties.
A toner composed of core particles completely coated with shell layers may exhibit poor releasability (i.e., inefficient elution of a release agent from the core particles) during fixation for high-speed printing (refer to, for example, Japanese Patent Application Laid-Open Publication No. 2014-048525).
In view of superior low-temperature fixing properties of a core-shell toner and high releasability of the toner during high-speed printing, components contained in core particles are required to be efficiently eluted to the surfaces of toner particles during fixation.